1. Field of the Invention
This invention relates generally to an apparatus and method for sequestering flue gas CO2 and, more particularly, the invention relates to an apparatus and method for sequestering flue gas CO2 having a fluidized bed reactor for simultaneously capturing and mineralizing coal combustion flue gas CO2,
2. Description of the Prior Art
Atmospheric CO2 (g) is indispensable for physical, chemical, and biological processes which occur in the atmosphere, hydrosphere, and geosphere of the planet Earth. During the past 150 years, atmospheric CO2 concentration increased approximately 30 percent, due to burning of fossil fuels containing carbon. For example, before industrial rapid growth, the atmospheric CO2 concentration was 280 ppm and the current CO2 concentration is 381 ppm. Increase in atmospheric CO2 concentration is typically attributed to the global warming and subsequent climate change problems.
Coal reserves are vital for providing global primary energy needs. Studies suggest that energy production from coal combustion process is also recognized for more than 50% of the increase in global CO2 levels in the atmosphere. Energy production from coal combustion power plants, like any other industrial process, results in various by-products, including flue gases (e.g., CO2, SOx, NOx) and solid wastes (e.g., fly ash and bottom ash). The new Clean Air Act enacted by the U.S. Congress mandated the reduction of SOx emissions from coal burning power plants. As a result, varieties of Clean Coal Technologies (CCTs) are developed and implemented. Applications of CCTs result in production of alkaline CCT ash with pH ranging from 9-12. In addition, there has been much discussion recently on proposals to reduce atmospheric CO2 emissions, possibly by enacting carbon taxes.
Currently several techniques exist to capture CO2 from coal combustion processes:                Pre-combustion methods (fuel decarbonization);        Combustion in O2/CO2 atmospheres (oxy-fuel firing); and        Post-combustion capture methods.However, all of the above techniques have their own drawbacks. For example, these techniques are energy extensive and produce additional by-products which require special handling and disposal methods.        
Several journal articles on the CO2 (g) infusion technique (carbonation process) for alkaline solid wastes have been published. These carbonation studies were conducted in an attempt to speed up the natural carbonation process as well help protect the environment (air, surface water, soil, and groundwater). The studies suggested that since the carbonation process uses CO2, which can be obtained from the coal combustion process itself. Another potential benefit is that the carbonation process could help capture and minimize CO2 emissions into the atmosphere. However, previous batch laboratory experiments have experienced diffusion limitations—that is, the CO2 may not efficiently contact the ash sample. In addition, nothing exists to simultaneously capture and mineralize coal combustion flue gas CO2 with fly ash or bottom ash under actual plant combustion conditions.
Accordingly, there exists a need for an in-plant use to capture and mineralize flue gas CO2 for both reducing flue gas CO2 emissions and stabilizing ash.